1. Field of the Invention
The present invention generally relates to a sensor, and more particularly to an active infrared presence sensor.
2. Description of the Related Art
Electrical energy can be saved by automatically powering down computer terminals and associated hardware during periods of inactivity. This is often done by detecting a lack of input activity (e.g., inputs via keyboard, mouse, etc.) for some predetermined period of time, with power being restored when activity resumes.
However, this is unsatisfactory for certain applications, such as point-of-sales (POS) terminals, because of the delays and/or extra keystrokes. It is also annoying to have a terminal power-down when one is seated in front of it. Further, it is unacceptable for unattended walkup kiosks, as this would require an untrained customer to first recognize that the kiosk was actually operational but in a power-down state, and then initiate the power-on state.
In both cases, a better solution is to directly sense the presence or absence of an operator. Very generally, such detectors can be characterized as sensing either motion or presence of a user. Presence sensors are preferable for a POS or other terminal where the operator may be seated, as it is then possible to be nearly motionless for an extended period of time. Either type of sensor can be used for a walkup kiosk.
An additional requirement for either a presence or motion sensor is that it be capable of discriminating between the operator and a random passerby or even a nearby stationary object. Thus, a sensor with well-controlled range and directional properties is required.
Yet another requirement is very low cost. This requirement suggests using components which are mass-produced for a much larger market. A final requirement is to provide a method to adjust the sensing range to accommodate various physical arrangements, preferably one which can be performed by unskilled personnel.
Although presence sensors can be built using ultrasonic, electrical, and optical radiators and detectors, currently it appears that the goal of very low cost can be met best by using a narrow-beam infrared (IR) emitter to direct IR radiation towards the operator position, and an infrared detector to measure the return radiation reflected from the operator.
Such a system was described in xe2x80x9cActive Infrared Presence Sensorxe2x80x9d, J. Levine and M. Schappert, IBM Technical Disclosure Bulletin (TDB), Volume 37, No. 12, page 419 (December 1995), which is hereby incorporated by reference. This sensor made use of a low-cost IR detection module intended for use in remote control systems. However, this sensor lacked certain beneficial features and improvements of the present invention as described below.
That is, prior to the present invention, there was no known solutions to the problem of on/off xe2x80x9cchatteringxe2x80x9d when the operator was positioned at the edge of the detection range. In other words, the sensor lacked range hysteresis. Further, there was no low-cost and easily manufactured mounting arrangement. Such an arrangement must provide cleanable windows which protect the optical components, maintain the integrity of the display covers (e.g., against contamination such that the covers are sealed well enough to be spill-resistant), and do so while preventing excessive coupling between the IR emitter and detector.
In view of the foregoing and other problems, drawbacks, and disadvantages of the conventional methods and structures, an object of the present invention is to provide a very low cost presence sensor to detect a stationary operator.
It is a second object of this invention to provide a presence sensor with angular response limited to the expected angular position and size of a display operator.
It is a third object of this invention to provide a presence sensor having a precise detection range, the range being adjusted automatically when desired by unskilled personnel.
It is a fourth object of this invention to provide a presence sensor having range hysteresis, so that the output signal does not chatter between on and off.
It is a fifth object of this invention to provide a low-cost mechanism for integrating such a presence sensor into the bezel of a display terminal in a way which allows cleaning and touching of the terminal while protecting the sensor from damage, maintains the integrity of the terminal (e.g., against contamination), and avoids direct coupling of IR radiation from the emitter to the detector.
In a first aspect of the present invention, a presence detector includes an optical emitter for emitting optical radiation, an optical detector for detecting a presence of an object based on receiving reflected optical radiation, and a microcontroller for controlling the optical emitter and processing the output of the optical detector, such that a range adjustment and range hysteresis based on the object are provided by software in the microcontroller.
In a second aspect, a display terminal includes an optical emitter for emitting optical radiation, an optical detector for detecting a presence of an object based on receiving reflected optical radiation, and a microcontroller for controlling the optical emitter and processing the output of the optical detector, such that a range adjustment and range hysteresis based on the object are provided by software in the microcontroller.
With the above and other unique and unobvious aspects, the invention uses a modulated light emitting diode (LED) which emits infrared radiation (IR) over a narrow range of angles centered on the expected location of a terminal operator. Infrared radiation is preferred over visible radiation because it is not distracting, and is less likely to be absorbed by clothing. The radiation reflected from the operator is detected by an IR detection module intended for use in remote control receivers (e.g., VCR or TV). A small microcontroller drives the LED with a pulse sequence optimized for detection by the module. The digital output of the module is processed by the microcontroller to determine the presence or absence of an operator and to provide a power-down control signal to the POS terminal.
Processing includes noise reduction, and the prevention of rapid on/off cycling when an operator is at the edge (threshold) of the detection range. This is done despite the use of modules which lack any external adjustment and provide only a logic level (0 or 1) output signal in response to infrared input. Range calibration service is also provided by the microprocessor via a digital input command signal.
The major difficulties to be overcome are associated with the low-cost detection modules. These are completely self-contained and have no adjustable parameters. In particular, they operate at a fixed modulation frequency, bandwidth, and detection threshold. Further, they feature an automatic gain control which gives them a very large dynamic range. At low signal levels, the gain is very high and the detection threshold is fixed at a level such that the signal-to-noise ratio (SNR) is low. This is not a problem in their intended application, as the threshold corresponds to a one-way range of tens of meters, well beyond the usual operating range for VCR remote control units.
That is, in normal use, the gain is automatically reduced to a level such that the SNR is very high. Noise is a problem in the current application because presence detection inherently occurs when the signal is just strong enough to be detected (i.e., cross the threshold). At this level, the gain is very high and the SNR is low.
As a result, some form of post-detection filtering is useful for reliable presence sensing. Such filtering is made difficult by the fact that, as noted above, the only available output signal is a logic level which changes from 1 to 0 when the correct pulse sequence (see below) is detected. It is further complicated by the very low-cost microcontroller, which is fast but has a very limited instruction set.
Another advantage is that the range can be adjusted by the operator without assistance. This would be difficult or impossible if the operator had to first position himself at the desired range and then reach out with a screwdriver to adjust a variable resistor. That is, even if the user could reach the screw, it is likely that the user""s arm would be detected.